The present invention relates to a navigation system that reads out map data from a plurality of storage media each having stored thereon map data about a particular area and provides navigation information on the optimum route to the intended destination for each area.
The navigation system is to direct the vehicle to the intended destination from the place where the vehicle is currently traveling (hereinafter referred to as a current vehicle position). On the user""s setting of his destination, the navigation system detects the current vehicle position by means of various sensors, and makes a search for the optimum route to the destination through utilization of the detected current vehicle position and map data prestored on each storage medium such as a CD-ROM (Compact Disk-Read Only Memory) or DVD-ROM (Digital Versatile Disk-Read Only Memory). And the navigation system displays, for example, the current vehicle position and the route to the destination on the road map displayed on a monitor and, at the same time, provides the navigation information in a computer-generated voice. At this time, the road map on the monitor as well as the current vehicle position thereon change every moment as the vehicle travels, and the voice message also changes accordingly.
On the storage medium there are usually prestored wide-area map data (rough map data describing the entire area of Japan or Europe, for instance) and detailed map data on a limited area (detailed map data describing the Kanto, Chubu or Kansai area of Japan, or each European country, for instance).
With a conventional navigation system disclosed, for example, in Japanese Patent Application Laid-Open Gazette No. 113296/97, when the vehicle travels from one area to another, for example, from Osaka to Shikoku in Japan or from France to Italy in Europe, rough navigation information on the route is given based on wide-area map data recorded on any storage media, whereas detailed information is derived from map data recorded on the storage media that describes the current vehicle position, the destination and intermediate areas.
With the conventional navigation system of the above configuration, when the vehicle travels out of the area described by the detailed map data read out of the storage medium loaded in a disk storage drive, detailed navigation information becomes difficult to present, and hence rough map data will be used instead. In practice, however, the user is often reluctant to switch the currently loaded storage medium to another for the new area until the information based on the rough map data actually imposes a considerable inconvenience on him. Thus, the conventional navigation system lacks operating ease in continuously providing appropriate navigation information over an extended route to the destination.
It is therefore an object of the present invention to provide an easy-to-use navigation system which, upon deciding that the current vehicle position is outside the area described by the map data being read out of the storage medium, provides an indication to make the user aware of the necessity for switching to a storage medium having stored thereon detailed map data on the area including the current vehicle position.
Another object of the present invention is to provide an easy-to-use navigation system which, upon deciding that the current vehicle position is inside the area described by the map data being read out of the storage medium, provides an indication to make the user aware of the necessity for switching to a storage medium having stored thereon map data on the area for which the vehicle is heading.
According to an aspect of the present invention, the navigation system makes a check to see if the current vehicle position is inside the area described by the predetermined map data being read out of the storage medium by the disk storage drive, and if not, gives an indication of the necessity for switching the current storage medium to another having stored thereon map data that describes the neighboring area including the current vehicle position. This creates awareness in the user about the necessity for switching to the above-mentioned another storage medium so as to obtain detailed navigation information. Accordingly, the navigation system of the present invention is cable of providing reliable information continuously over an extended route.
According to another aspect of the present invention, the navigation system makes a check to see if the intended destination is inside the area described by the predetermined map data being read out of the storage medium by the disk storage drive, and if so, gives an indication of the necessity for switching the current, storage medium to another having stored thereon map data that describes the neighboring area including the intended destination.
According to still another aspect of the present invention, the navigation system makes a check to see if the current vehicle position is in a predetermined place in the area described by the map data being read out of the storage medium by the disk storage drive, and if so, gives an indication of the necessity for switching the current storage medium to another having stored thereon map data that describes the neighboring area for which the vehicle is heading. This creates awareness beforehand in the user about the necessity for switching to the above-mentioned another storage medium so as to obtain detailed navigation information. Accordingly, the navigation system of the present invention is cable of providing reliable information continuously over an extended route.